1. Field of the Invention
The present invention generally relates to electromagnetic valves such as, for example, used in vehicle anti-lock braking systems and, more particularly, to improved electromagnetic valves having a relief for relieving an excessive hydraulic pressure when the hydraulic pressure received by a valve body exceeds a predetermined value when the valve body is closed by excitation of a coil.
2. Background Description
A known electromagnetic valve fitted with a relief means has been disclosed in, for example, Japanese Patent Publication No. 502473/1995. There, a series of guide holes is formed in a valve housing and the central portion of a fixed core. Hollow push bars, which are pushed forward when the coil is excited, are fitted in the respective guide holes. A valve body is slidably fitted in the hollow push bar and contains a relief spring for urging the valve body in the direction of the closing the valve. Furthermore, a valve spring for urging the push bar in the direction of opening the valve body is provided in the valve housing, whereas the push bar is fitted with a stopper for defining a limit to which the valve body is moved forward by the relief spring in the direction of closing the valve body. While the valve body is kept open by defining the limit to which the push bar is moved forward toward the valve body when the moving core is moved back, the valve body is allowed to be opened by a relief valve as the moving core moves forward. This electromagnetic valve demonstrates the relief function in that while the valve body is made to perform the normal opening-closing operation as the coil is excited or demagnetized in addition to the case where even in its closed state, the function of relieving the excessive hydraulic pressure is ensured by allowing the valve body to be opened by the relief spring. Therefore, special relief valves are not needed to be connected to such electromagnetic valves in parallel, so that the hydraulic fluid circuit is simplified further.
However, a valve housing having a relatively large diameter has to be formed because the valve body and the push bar are doubly arranged on the inside and outside of the valve housing and contained therein in the prior art and this has made it difficult to reduce the diameter size of an electromagnetic valve.